The present invention relates to a seat back for a vehicle with a one-piece supporting structure made of light metal alloy, with a frame having an essentially rectangular contour and defining the upper, the lower and the two lateral delimitations of the seat back.
Increasingly great demands are made upon seat backs for vehicles. On one side, a seat back must offer high structural integrity. This is particularly important when an anchor point for a seat belt is provided on the seat back, as this is desirable with cabriolets and minivans. Great stability under load is also required to improve crash safety. On the other hand however, high standards are required from a seat back as well as from other vehicle parts with regard to lightweight construction. Therefor, the supporting structure for such a seat back is increasingly often made of light metal. The alloys that are particularly in use are aluminum and magnesium alloys. It is particularly advantageous to make the supporting structure in one piece and to form it by pressure die-casting.
DE 196 30 288 A and DE 198 33 887 A present a supporting structure for a seat back consisting of a bordering frame surrounding a large central opening. Although such a frame offers some structural integrity, a big quantity of material is required to achieve enough rigidity in order to fasten the belt, which increases not only the weight but also the costs.
EP 881 116 A discloses a seat frame consisting of a plate bordered by a flange. One large central opening and several smaller openings are provided therein. Compared to the weight required, integrity as well as rigidity are unsatisfactory.
EP 0 244 785 A presents a back for vehicle seats, in particular for the rear seats of vehicles, that is provided with a cross-shaped sheet metal part. Here too, structural integrity is not sufficient.
The solutions disclosed in EP 0 646 493 A or in GB 2 246 699 cannot meet the requirements either.
The object of the invention is to provide the possibility to improve a vehicle seat of the type mentioned above in such a way that it weighs less while gaining in rigidity and in stability under load. Another object is to render production of the supporting structure as easy and inexpensive as possible.
The solution of these objects is to accommodate in the frame, in the vicinity of its diagonals, a cross-shaped reinforcement rib that is provided with rib structures arranged thereon in a grid-like configuration. Thanks to the solution according to the invention, two advantageous effects are obtained at the same time. One of them is that the cross-shaped reinforcement rib proved to be a very effective stiffener in particular for seat backs provided with an anchor point for a seat belt. The other is that the flow paths of the material can thus be shortened during the manufacturing process, which has a positive influence on quality and integrity. Still another advantage is that the reinforcement rib offers protection of the occupants from objects penetrating the vehicle from behind.
From a casting point of view, it is advantageous when the reinforcement rib is slightly curved. In order to prevent thermal tensions during the cooling process, which may cause undesired deformations or cracks, a slight curvature proved to be advantageous. Such a curvature can either be designed as an overall curvature, the reinforcement rib following the shape of a cylindric or of a spheric surface tentered within the frame or as a local curvature, in which the individual webs of the reinforcement rib have a curved section. The advantage of the overall curvature is that temperature stress can be reduced without a problem, whereas the local curvature is characterized by a specific rigidity.
A shape that is particularly suited for casting is obtained by providing the reinforcing rib with a central part from which one connecting web is projecting to either corner of the frame. In a particularly preferred embodiment, at least one connecting web is divided into two sections by a recess. As a result, the flow paths can be optimized, since the flow velocity is increased by reducing the cross section so that cooling of the melted mass during the casting process is reduced, which also brings about best integrity.
In a particularly preferred embodiment of the invention, the gating is accommodated in a recess constituted by the reinforcement rib and the frame. As a result, the overall dimensions of the casting mold can be kept small. It also proves particularly advantageous that the flow paths to the corners of the frame, which are particularly subject to load, are short and of about the same length. This can be particularly fostered by the fact that the gating preferably occurs in the central part of the reinforcement rib. The gate, that is the transition area between the gating and the work piece, has got the shape of a fan. On completion of the casting procedure, the gate is punched off. Another advantage of this solution is that a lordosis support can be accommodated in the finished seat in the relatively large recess provided for the gating.
The quality of casting can be improved further by arranging connecting ribs serving as flow aids on the transitions between the frame and the reinforcement rib.